1. Field of the Invention
The invention relates to a method and system for initializing a device, and more particularly to a method and system for transmitting initial state values via a bus during an initialization period.
2. Description of the Related Art
In an electronic system, such as a computer system, pins of a device (e.g., a chip) are used to design strapping functions in order to setup initial states of the device or enable the device to support additional functions. Strapping functions are configured to set the initial states, such as the frequency of a phase lock loop (PLL), the turned-on or turned-off state of a specific function (e.g., test mode of the device), and the setting of other functions.
Because there are numerous initial state values, if the number of pins reserved for the strapping functions is increased to setup the initial states, the size and manufacturing cost of the device are greatly increased. To avoid this problem, some general-function signal pins of the device are used to provide initial levels by pull-up or pull-down resistors. The device then latches these initial levels when effective transition edges of a system-power-completed signal occur, thus, the purpose of setup initial states is achieved. Because pads of the general-function signals are ti-state isolated, the values of the resistor are latched before the system power is completed (the system-power-completed signal is effective), thus, the initial levels are latched correctly. The pull-up or pull-down resistors, however, affect the quality of the general-function signals in a normal operation. Thus, the pull-up or pull-down resistors are only applied to lower frequency general-function signals.
FIG. 1 is a block diagram of a conventional electronic system 10 with strapping functions. The electronic system 10 comprises a first device 11 and a second device 12. The strapping functions are applied in general-function signals S1 to Sn between the first device 11 and the second device 12. The general-function signals S1 to Sn are selectively pulled up or down by jumpers J1 to Jn, respectively. The second device 12 comprises a system-power-completed signal Power_OK. FIG. 2 is waveform diagram of the signals when the second devices 12 perform the strapping functions. As shown in FIG. 2, when the system-power-completed signal Power_OK is transited to an effective rising edge, the pulled-up or pulled-down values of the general-function signals S1 to Sn are latched. The general-function signals S1 to Sn, however, can only provide n bits initial values to be setup. Moreover, pulling resistances up or down affects the quality of general-function signals S1 to Sn in a normal operation.